7 erasers cost $8.05. Which equation would help determine the cost of 11 erasers?
Explanation: There are several equations that could help determine the cost, each with a slightly different approach. We know the cost of 7 erasers. We want to know the cost of 11 erasers. We can write the numbers of erasers as a proportion: $\dfrac{7}{11}$ We know 7 erasers costs $8.05. We can let $x$ represent the unknown cost of 11 erasers. The proportion of these costs can be expressed as: $\dfrac{\$8.05}{x}$ The cost changes along with the number of erasers purchased, and so the two proportions are equivalent. $\dfrac{7}{11} = \dfrac{\$8.05}{x}$